Mechanisms of Slab Contributions in Beam-Column Subassemblages


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Title: Mechanisms of Slab Contributions in Beam-Column Subassemblages

Author(s): P. C. Cheung, T. Paulay, and R. Park

Publication: Special Publication

Volume: 123


Appears on pages(s): 259-290

Keywords: beams (supports); columns (supports); cyclic loads; ductility; earthquake-resistant structures; frames; hinges (structural); slabs; joints (junctions); reinforced concrete; shear strength; tests; structural design; Structural Research

Date: 1/1/1991

Proposes mechanisms of the transfer of forces to beam-column joints, generated under typical seismic actions in cast-in-place reinforced concrete slabs. One of the main objectives of the paper is to review behavioral models that should assist designers in visualizing the flow of internal forces in beam-column-slab subassemblages. It is postulated that membrane forces play a dominant role and that contributions of other actions, such as bending in slabs and torsion in transverse beams, are relatively unimportant, particularly when significant ductility demands arise during seismic motions. Locations at which slab reinforcements transmit tensile forces by means of bond to the surrounding concrete are considered to be particularly important in the assessment of the enhancement of beam flexural strength. The description of these phenomena is related to observations made during the testing of isolated reinforced concrete beam-column subassemblages with slabs simulating one-and two-way cast-in-place floor systems. Subsequently, the findings are extended to describe the perceived behavior of continuous floor slabs supported by beams of multibay ductile frames. The relevance of the flexural strength enhancement of beams to the design of beam-column joints and columns is briefly examined. Design recommendations are made, particularly with respect to the effective width of the tension flanges.